Variations on Advanced Sudoku Logic Puzzles (Vol 1) 
 Chapter 33: Four Easy Sudoku-15up Puzzles (numbers 107-110) 
 
-  Step-by-step instructions for solving  Puzzle 107, (75/225)   Diff: 3/991
 -  Step-by-step instructions for solving  Puzzle 108, (75/225)   Diff: 4/9942
 -  Step-by-step instructions for solving  Puzzle 109, (82/225)   Diff: 4/9932
 -  Step-by-step instructions for solving  Puzzle 110, (85/225)   Diff: 4/9955